A new batch of Jupiter images from NASA's Cassini spacecraft was released Tuesday, revealing various closeups, including a crisp shot of the Jovian moon Io seemingly floating close to the gas giant.

The Galilean satellite Io floats above the cloud tops of Jupiter in this image above, captured on Jan. 1, 2001 10:00 UTC, two days after Cassini's closest approach. The image is deceiving: there are 217,000 miles (350,000 kilometers) -- roughly 2.5 Jupiters -- between Io and the Jovian clouds. Io is the size of our Moon, and dwarfed by Jupiter.

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These color composite frames were acquired on Dec. 31, 2000. The left is a composite that shows Jupiter's color as seen by the naked eye. The right frame is composed of various images, including some taken through narrow-band filters that show where the gaseous methane in Jupiter's atmosphere absorbs light. The image shows colors that denote the height of the clouds. Red regions are deep-water clouds, bright blue regions are high haze. Small, intensely bright white spots are energetic lightning storms that have penetrated high into the atmosphere. The darkest blue regions are the very deep 'hot spots' from which Jovian thermal emission is free to escape to space.

These images taken through Cassini's wide-angle camera near closest approach in the deep near-infrared methane band, combined with filters that sense electromagnetic radiation of orthogonal polarization, show that the light from the poles is polarized. That is, the poles appear bright in one image and dark in the other. Polarized light is most readily scattered by aerosols. These images indicate that the aerosol particles at Jupiter's poles are small and likely consist of aggregates of even smaller particles, whereas the particles at the equator and covering the Great Red Spot are larger. Images like these will allow scientists to measure the distribution, size and shape of aerosols, and consequently, the distribution of heat, in Jupiter's atmosphere.

NASA's $3.4 billion Cassini spacecraft is presently in a six-month flyby of Jupiter during a gravity-assisted swing toward Saturn and a four-year long study of the ringed planet that will begin in July 2004.

Cassini made its closest pass to Jupiter on Dec. 30, 2000, gaining a gravitational boost for reaching its main destination, Saturn, in 2004. It will continue to make observations and measurements of the Jupiter system through March 2001.

Researchers are using the Jupiter flyby as an opportunity to try out some of Cassini's advanced instrumentation.

"Every new spacecraft carries instruments that expand our ability to see things," said Stamatios Krimigis, space department head at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland and principal investigator for the Magnetospheric Imaging Instrument (MIMI) aboard Cassini. "With MIMI, we're able to visualize the invisible."

The MIMI instrument includes an Ion and Neutral Camera developed by the Applied Physics Laboratory (APL), a spectrometer built by the University of Maryland under Douglas Hamilton and a high-energy particle detector developed by Stefano Livi of APL and a number of co-investigator institutions.

"By detecting various energetic particles and discriminating among them according to energy and mass, the camera is able to obtain remote images of the global distribution of these particles," said Donald Mitchell of APL, who leads the camera science team.

From a distance of 6 million miles (9.7 million kilometers), MIMI's camera has recorded pictures of Jupiter's energetic particle-filled magnetosphere.

The images, said Krimigis, "reveal that the particles we're detecting -- primarily hydrogen, but also oxygen, sulfur and sulfur dioxide -- are spewed from volcanoes on the Jovian moon Io and spun out into Jupiter's magnetosphere, where they are trapped, energized and accelerated to high velocities. Then, when collisions with other particles provide them with an electron, they become neutral and are able to escape the magnetosphere. And that's when we can detect them with our camera."

In addition to imaging the Jovian magnetosphere, MIMI's instruments have also detected the presence of a huge nebula of particles enveloping Jupiter and extending out to at least 13 million miles (22 million kilometers) from the planet, according to Hamilton, the developer of another MIMI sensor that detected oxygen, sodium, sulfur, potassium and sulfur dioxide.

"All of these are constituents of the gas spewed out by Io's volcanoes, thrown out of Jupiter's magnetosphere and eventually picked up by the flowing solar wind," said Hamilton.